Rhodium-Catalyzed Reaction of Sulfoxonium Ylides and Anthranils toward Indoloindolones via a (4 + 1) Annulation.

A rhodium-catalyzed annulation between aroyl sulfoxonium ylides and anthranils has been developed to synthesize 10H-indolo[1,2-a]indol-10-one derivatives. This reaction started with an unpredented (4 + 1) annulation toward N-(2-formylphenyl) indolones, proceeding with the sequential ortho-amination of the C-H bond in aroyl sulfoxonium ylides by anthranils and the insertion of N-H to carbene. Finally, the Aldol condensation constructed the second indole ring. This procedure features the formation of two C-N bonds and one C═C bond in one pot.